The last time we had as many posts on a single day as we did yesterday was June 22nd, 2008 - I'm guessing the Ciddies. I imagine the CK contest also helped, but...

The last time we had as many active users logged in on a single day as we did yesterday was April 14, 2008 (that one wasn't a Ciddies spike, either, we just had that many users around then).

I declare my email a resounding success!